Worms in Dogs

Just about every dog on the planet is infested with worms to some degree. If they stay at low levels, your dog can build up immunity to them. But if the infestation reaches a certain point, worms can cause anemia, lethargy, poor appetite, and even death. Fortunately, almost all worms can be detected by a vet and treated with medication.

It seems there’s no end to the kinds of worms out there (or in there). Among the most well known:

There are others, including protozoans, flukes or trematodes, ascadis (a kind of roundworm), threadworms (also a roundworm), stomach worms (found mostly in the southeastern U.S.), eyeworms, and lungworms.

You’ve probably lost your appetite by now.


These often-microscopic parasites are all around us, but they usually enter a dog’s body when he eats infected feces, soil, carrion, or raw meat. It’s probably impossible to completely prevent infestation, no matter how spic and span you keep your dog’s environment, but simple hygiene, common sense, and widely available medications can all help.


Each worm has a slightly different means of making its way into your dog’s body and a different set of symptoms, some more serious than others.

Roundworms are transmitted when dogs eat dirt or feces contaminated with roundworm eggs. Nearly all puppies are born with roundworm–most mothers have dormant larvae in their tissue. These larvae come to life at the end of the pregnancy and migrate into the lungs of the new pups. At their worst, roundworms can cause liver damage or intestinal blockage, and even a light infection can result in a dull coat, dry skin, and a potbelly. (Humans can get roundworm, too, so–as if you need reminding–always wash your hands after handling dog feces, and don’t allow children to play near soil where dogs have pooped).

Hookworms are the most common parasite in the U.S., at least among dogs. About one dog in five has them right now. They’re named for the hooklike teeth they use to attach themselves to the dog’s intestinal lining, and are transmitted from infected feces or even directly through the skin when the dog walks through wet grass or on sand where the larvae are active (that’s one of the reasons dogs aren’t allowed on most beaches). Humans can be hosts for hookworms, too. Symptoms include diarrhea, weakness, and–in severe cases–anemia.

Whipworms are transmitted by ingesting eggs that live in the soil. The dirt gets on paws, on toys, or on food and water dishes, and the dog takes it in. The most common problem is recurring diarrhea caused by the inflammation of the intestine. Serious cases can also cause anemia, dehydration, lethargy, and weight loss. Fortunately for dog owners, this worm doesn’t affect humans.

Tapeworms are long, segmented worms that live in the small intestine. They come in several varieties and are transmitted through infected soil, from ingesting fleas while self-grooming, or even from eating rodents. Tapeworms usually cause very little harm except in severe cases, when the dog might suffer from abdominal pain, nervousness, weight loss, vomiting, or severe itching around the anus (and there’s nothing quite as disgusting as finding a tapeworm segment on the sofa or chair after your dog has been lying there). They’re most common among hunting dogs, as well as cats.

Heartworms are among the most dangerous worms; they can seriously damage a dog’s heart and lungs and can be fatal if left untreated. They’re transmitted through mosquito bites (from a mosquito that’s just visited another infected dog, and brings the larvae with it). Symptoms include coughing, diminished strength, and lethargy. Untreated, heartworm can cause high blood pressure, obstructions in the heart, and even heart failure.

When it’s time to see a vet

You may very well see worms in your dog’s feces–but that doesn’t necessarily mean your dog’s sick. Many dogs are born with worms already in their system, and they’ve built up an immunity to them. However, if you notice a change in your dog’s health, then it’s time for a visit. Those changes could include:

Your vet will run a series of tests on your pet’s blood and stool and decide if and how to treat the infestation. This is true for puppies as well; most puppies are infested with roundworms and other parasites from birth or shortly thereafter, and only a vet is equipped to detect and treat them all.

What’s next

Prevention is always the best approach, so have your adult dog’s stool checked for worms once a year (remember, you can’t always see the worms if you examine the stool yourself). Yes, those annual trips to the vet can be expensive, but not nearly as expensive as treating your dog for a serious infestation.

If your dog has been infected, over-the-counter worm medications aren’t always the best solutions. Many are effective only against one kind of parasite and require repeat treatments over a long period of time–it all depends on the worm and the level of infestation, as well as the age and general health of your dog. (In some cases, like tapeworm, prescription meds are the only thing that’s at all effective.) A vet can give you a better idea of what will work in your dog’s particular case. Treatment isn’t usually all that traumatic; for most cases, oral medications will do the job.

Since many worm infestations are regional and seasonal, it’s a good idea to ask your vet about what combination of over-the-counter meds (if any) your dog needs and how often he should be checked for worms.

How to prevent worms

Preventive medications such as Sentinel and Heartgard Plus work very well, but it’s always possible for the worms to make a comeback. To keep that from happening, you have to destroy eggs or larvae before they reappear. That means good sanitation and a clean, dry living space for your pet:

  • Outdoor runs should have a watertight surface (of cement, for instance) instead of dirt.
  • Scoop poop from the yard or run daily.
  • Keep your lawn cut short and water it only when necessary.
  • Fleas, lice, mice, and other rodents can carry tapeworm and pass it on to your dog. Get rid of them and you’ll control the disease.
  • Don’t let your dog roam and hunt; raw meat, carrion, or parts of dead animals that are likely carriers of parasites.
  • If you give your dog any fresh meat, be sure to cook it thoroughly first.

Related articles:

Heartworm in dogs

Parasite prevention

Treating internal parasites